Machine tool

ABSTRACT

A machine tool of small scale, light weight, and low cost, yet accomplishing a high degree of precision in machining. A spindle ( 2 ) is encased in a body frame ( 1 ) and disposed preferably in such a manner that the spindle ( 2 ) is movable along an axial center thereof or Z-axis direction by means of a Z-axis moving means ( 4 ). Either Y-axis table ( 5 ) or an X-axis table ( 6 ), at least being capable of moving along X-axis or Y-axis direction, or both is provided at one end of the spindle ( 2 ) on one side of the body frame ( 1 ) and arranged to be vertical with respect to the axial center of the spindle ( 2 ).

TECHNICAL FIELD

The present invention relates to a machine tool.

BACKGROUND ART

In a conventional machine tool with a vertical spindle, the spindle issupported by a column in such a way that the spindle is movable alongits axial direction or the Z-axis, and the column is either directly orindirectly supported on a base. In an exemplary arrangement shown inFIG. 21(a), an X-axis table 72 being movable in the X-axis direction ismounted on a base 71, and a column 73 serving as a Y-axis table beingmovable in the Y-axis direction is mounted on the X-axis table 72. Aspindle head 74 is supported by the column 73 movably along the Z-axis,and a work bed 75 is connected to the base 71. In another arrangementshown in FIG. 21(b), an X-axis table 76 serving as a work bed and thecolumn 73 serving as a Y-axis table for movement in the Y-axis directionare mounted on the base 71. The spindle head 74 is supported by thecolumn 73 movably along the Z-axis direction. U.S. Pat. No. 5,439,431typically discloses such type of machine tool, in which a spindle drivento move in Z-axis direction is mounted on a compound slide(corresponding to the column 73 in FIG. 21(b)) which is moved in X-and/or Y-axis direction. In yet another arrangement shown in FIG. 21(c),an X-axis table 78 serving as a work bed being movable in the X-axisdirection is mounted on a Y-axis table 77 for movement in the Y-axisdirection, which is disposed on the base 71. A column 79 of an invertedL shape is vertically mounted on the base 71, and a spindle head 80having a built-in mechanism for movement in the Z-axis direction ismounted to the distal end of the column 79. In a still further exampleshown in FIG. 21(d), the Y-axis table 77 is mounted on the base 71 formovement in the Y-axis direction, and the X-axis table 78 serving as awork bed is mounted on the Y-axis table 78 for movement in the X-axisdirection. A column 81 is vertically mounted on the base 71, and thespindle head 74 is supported by the column 81 movably along the Z-axis.

Other types of machine tools such as the one employing a gate-likecolumn (not shown) or the one having its spindle arranged horizontallyhave substantially the same configuration as described above.

The spindle head is generally cantilevered by the column in any of theprior arrangements described above. In order to variably determine thepositional relationship between the spindle head and the workpiece, themechanisms that link the spindle head and the work piece are constructedto detour the space therebetween. To accomplish high-speed and highlyprecise machining, the machine tool must meet two requirements. Firstly,the materials constituting the base, table, column, and other membersshould be given high rigidity. Secondly, the play between moving partsof each member should be minimized. To meet these requirements,relatively larger members precisely constructed are necessary, causingthe entire machine to be larger, heavier, more expensive, and to occupya larger space in a factory line for installation.

Another problem is attributable to the detoured structure and the largescale of the entire machine. Thermal deflection caused by changes intemperature has greater influence on the mechanisms, adversely affectingthe precision of machining.

In view of the foregoing, it is an object of the present invention toprovide a machine tool which accomplishes a high degree of precision inmachining with minimized size, weight, and cost.

DISCLOSURE OF INVENTION

In order to accomplish the above-said object, a machine tool accordingto the present invention is characterized in that the spindle issupported at both sides within a stationary box-like body frame whichconstitutes a main frame of the machine body and located approximatelyat the center of the machine body, and that an X-axis table and a Y-axistable being respectively movable along X-axis and Y-axis directions areprovided on a top face or one of four sides of the body frame andtherewith in a plane, which lies orthogonal to the axis of the spindlein such a manner as to be cumulated on one another, the chuck meansbeing mounted on the upper one of the X-axis table and Y-axis table.

Relative positions between the chuck means and the spindle is variablydetermined by moving the table disposed on one side of the body framewith respect to the axial center of the spindle disposed within the bodyframe. The mechanism for variably determining the positionalrelationship between the spindle and a workpiece held by the chuck meansis comprised of the body frame and the table on one side thereof inabutment with each other, and includes no roundabout members such as acantilevered column, providing no spaces between each member. The entiredesign of the machine tool can be thus compactly constructed with smalland light parts yet keeping high rigidity. High-speed and highlyaccurate machining is thereby accomplished while minimizing thestructure in size, weight, and cost. Further, the entire structure ofthe machine tool can be made approximately symmetrical around thespindle as the axis of symmetry, which restrains adverse effects ofthermal deflection caused by changes in temperature which leads toerrors in machining. It is to be understood that the axial center of thespindle may be arranged parallel as well as vertical to a horizontalplane.

In the above structure, the spindle is fixed to a Z-axis moving meanswhich is slidably supported on guide rails within the body frame formoving the spindle in Z-axis direction. Since the spindle is movable inonly one axial direction, the structure is simplified yet constructedwith high rigidity and precision. The workpiece can also be accuratelypositioned by controlling each table.

The machine tool according to the present invention may further comprisea base plate provided on the top surface or the projected part of thebase plate on one side of the body frame, contributing to a compactarrangement of the machine.

The machine tool according to the present invention may further compriseone or more tables disposed above the body frame, wherein the spindle isarranged to have the axial center thereof along a vertical direction andmounted with a cutting tool, and the chuck means is designed to hold theworkpiece upside down. As the workpiece is held downward, chips createdwhile machining flow down into an enclosed space in the body frame bygravity and effectively collected.

The spindle may be built in a high-speed motor as a rotary driverthereof and rotatably supported by non-contact type bearings. Themachining force can be reduced by the high speed operation of about40,000 rpm, and each member constituting the machine is required to haveless rigidity yet assuring precise machining. The entire structure ofthe machine can be thereby minimized in size, weight, and cost.

The non-contact type bearings may be magnetic radial bearings. Thespindle can be thereby readily and accurately supported by the controlof electromagnet.

The machine tool may further comprise a means of correcting any errorsin machining the workpiece by adjusting supporting position of thespindle by the non-contact type bearings. Errors created by inertialforce when the X-axis or Y-axis table changes its directions or causedby backlash are preliminarily measured, so that the correction is madeby the non-contact type bearings and it is unnecessary to correctnumerical control data for machining.

A chuck rotating means may be provided to cause the chuck means torotate around the axial center thereof. Circular parts of the workpiececan be precisely machined by rotating the workpiece instead ofcontrolling the movement of the X-axis or Y-axis table.

The body frame may be constructed to have a U-shaped cross-section. Thespindle or the rotary driver can be easily accessed from an opened sideof the body frame for assembly or maintenance.

The machine tool may be provided with a position sensor for detectingpositions of the workpiece held by the chuck means. When the workpieceis machined by several different machine tools in a plurality ofmachining processes, the workpiece can be precisely held by detectingany errors of the machine itself or errors in holding the workpiece bythe sensor.

The machine tool may further have a cutting oil applying means forejecting cutting oil from a side of the opening toward the workpiecebeing machined, and a collecting hopper for gathering the cutting oiland chips flowing down thereto. The cutting oil can be assuringlysupplied to the workpiece being machined, as well as the cutting oil andchips can be effectively collected.

A splash guard hood may be further provided around the chuck means forcausing the cutting oil splashing around the workpiece being machined toflow down into the collecting hopper. The cutting oil and chips can bethereby effectively collected.

The machine tool according to another embodiment of the presentinvention may have a sealing means to seal a gap between the splashguard hood and the collecting hopper while allowing a respectivemovement with each other therebetween. It is thus prevented that thecutting oil and chips splash around through the gap between the splashguard hood and the collecting hopper. When used in combination with avacuum suction means, collecting capacity is further enhanced by thevacuum pressure.

A collecting fluid applying means may be further provided for ejecting acollecting fluid toward into the collecting hopper, which is connectedto a collecting duct. The cutting oil and chips can be smoothlycollected by the fluent collecting fluid.

The collecting hopper may be arranged eccentrical with respect to theopening, and the collecting fluid applying means may be disposed in sucha way that the collecting fluid is blown from a side where a gap betweenthe periphery of a rotary driver for rotating the spindle and thecollecting hopper is narrow toward a widely-gapped side, where thecollecting duct is connected to the collecting hopper, so as to evenmore smoothly collecting the cutting oil and chips.

The collecting duct connected to the collecting hopper may be furtherconnected to a vacuum suction means. The cutting oil and chips can beassuringly collected without leaving any residuals thereof.

The cutting oil applying means may comprise three or more cutting oilejecting nozzles disposed to surround the workpiece being machined.Cutting oil can be thereby supplied to every part of the workpiece.

An on-off controller may be further provided for controlling ejection ofthe cutting oil from each cutting oil ejecting nozzle in accordance withthe position of the workpiece. As it is controlled to select propernozzles to be effective for blowing out the cutting oil, an oil pump ofsmall scale can supply a sufficient amount of the cutting oil.

In a machine tool according to the present invention, a corner of agiven radius is machined by numerical control using a cutting tooldesigned to machine a corner of the minimum radius. Every cornered partof the workpiece having several different radii can be machined by asingle cutting tool, assuring preciseness in machining as it is notnecessary to change cutting tools.

According to another embodiment of the present invention, a plurality ofspindles may be arranged in the body frame, and a plurality of chuckmeans may be disposed on the table(s). Productivity is thereby increasedas the workpiece can be simultaneously machined in plurality.

Also, the spindle may be provided in the body frame in singularity whilea plurality of the chuck means are disposed on the table(s). This allowsa plurality of workpieces to be fed to or received from the chuck means.Productivity is thereby increased as the time for exchanging workpiecesis reduced.

Alternatively, a plurality of spindles may be arranged in the body framewhile the chuck means is disposed on the table(s) in singularity.Several machining processes can be carried out in a single machine tool,whereby productivity is increased.

Further, a pair of chuck means may be disposed in the X-axis table inparallel with each other along the Y-axis direction, and the Y-axistable may be arranged to be movable between farthest ends where onechuck means positions just above the opening in the base plate, the baseplate having a pair of another openings through which a workpiece ifremoved from and fed to the other chuck means when the Y-axis table islocated at a given farthest end. While a workpiece held by one chuckmeans is being machined, another workpiece can be removed from and fedto the other chuck means, which reduces the time for exchangingworkpieces, thereby increasing productivity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a schematical perspective view showing the entireconfiguration of a machine tool according to the present invention, and

FIG. 1(b) is a control block diagram thereof.

FIG. 2 is an elevational vertical section view thereof.

FIG. 3 is a vertical side elevation view thereof.

FIG. 4 is a top plan view thereof.

FIG. 5 is a plan view of a horizontal section of a body frame in theembodiment.

FIG. 6 is a vertical side elevation view showing a modification of theembodiment.

FIG. 7 is a vertical sectional view showing a workpiece machining unitof the embodiment.

FIG. 8 is a bottom view thereof.

FIG. 9 is an explanatory view showing an arrangement of a cutting oilsupply control unit for supplying cutting oil to nozzles in theembodiment.

FIG. 10 is an explanatory view of a machining process of a cornered partof a workpiece in the embodiment.

FIG. 11 is a vertical sectional view showing a spindle and a rotarydriver of the embodiment.

FIG. 12 is an explanatory view showing an arrangement of a magneticradial bearing of a rotary driver and its controller of the embodiment.

FIG. 13 is an explanatory view showing how a quadrant projection iscreated during machining operation in the embodiment.

FIG. 14 is a flow chart of controlling the radial magnetic bearings toprevent the quadrant projection in the embodiment.

FIG. 15 is a front view showing a chuck rotating means of a secondembodiment of the present invention.

FIG. 16 is a vertical sectional view showing a cutting oil collectingunit of a third embodiment of the present invention.

FIG. 17 is an explanatory view showing a machining process of a fourthembodiment of the present invention.

FIG. 18 is a vertical sectional view of a machine tool according to afifth embodiment of the present invention.

FIG. 19 is a vertical sectional view of a machine tool according to asixth embodiment of the present invention.

FIG. 20 is a vertical sectional view of a machine tool according to aseventh embodiment of the present invention.

FIGS. 21(a)-(d) are perspective views showing various prior arrangementsof a conventional machine tool.

BEST MODES FOR CARRYING OUT THE INVENTION

Preferred embodiments of the invention will be hereinafter describedwith reference to the accompanying drawings.

FIG. 1(a) is a perspective view which schematically shows the entireconfiguration of the present invention. In FIG. 1(a), a box-like bodyframe 1 of approximately a rectangular parallelepiped encases a spindle2 standing upright along a Z-axis perpendicular to a horizontaldirection, a rotary driver 3 for driving the spindle 2, and a Z-axismoving means 4 for moving the spindle 2 and its rotary driver 3 alongthe Z-axis direction. On the top surface of the body frame 1 is a Y-axistable 5 being movable along the Y-axis, on which an X-axis table 6 ismounted for movement along the X-axis. A chuck means 7 for holding aworkpiece is disposed on the X-axis table 6. The Z-axis moving means 4,the Y-axis table 5, and the X-axis table 6 are operated through anumerical control device 60 as shown in FIG. 1(b).

Referring now to FIGS. 2 to 6 showing more detailed configurations ofthe first embodiment, the body frame 1 comprises a main frame 10cubically constructed by plates and placed on top of a bottom frame 9,which has adjustable support legs 8 on the bottom at all four corners. Abase plate 11 is placed on top of the main frame 10. As shown in FIG. 5,a horizontal sectional view of the main frame 10 appears approximatelyU-shaped. A high-speed motor as the rotary driver 3 including thebuild-in spindle 2 therein is approximately centered in the main frame10 and fixed to the Z-axis moving means 4. Since the main frame 10 isconstructed to have a U-shaped cross section, i.e., as one of the foursides of the frame 10 is opened, the rotary driver 3 and the Z-axismoving means 4 are readily accessed for assembling operation ormaintenance.

The Z-axis moving means 4 comprises a movable member 14 slidablysupported via a slide block 13 by a guide rail 12 along the Z-axisdirection. A screw feed shaft 15 is disposed parallel to the guide rail12 and rotatably supported by bearings 16 at both ends thereof. A nutmember 17 fixedly coupled to the movable member 14 is mated with thescrew feed shaft 15, which is driven to rotate by a Z-axis drive motor18. As the screw feed shaft 15 is rotated, the nut member 17 is movedalong the screw feed shaft 15, causing the rotary driver 3 fixedlymounted on the movable member 14 to slide along the Z-axis.

The base plate 11 has an opening 19 opposed to the spindle 2, throughwhich the machining operation is carried out. The base plate 11 islaterally extended from the main frame 10 toward one direction along theY-axis by an appropriate length, and the projected part has an opening20 for passing through a workpiece 30. It will be further advantageousif the base plate 11 is extended widely enough to be able to hold theY-axis table 5 thereon, in which case the space above the opening 19 onthe main frame 10 will be more broadly opened, which will facilitate theexchanging operation of a cutting tool 2 a at the tip of the spindle 2.

The Y-axis table 5 is slidably supported via a slide block 22 by a pairof guide rails 21 along the Y-axis direction arranged on either side ofthe base plate 11. A screw feed shaft 23 is provided in parallel withthe guide rails 21 at one side of the base plate 11, and rotatablysupported by bearings 24. A nut member 25 fixed to the Y-axis table 5 ismated with the screw feed shaft 23, which is driven to rotate by aY-axis drive motor 26 to cause the Y-axis table 5 to move along theY-axis direction.

The X-axis table 6 is slidably supported via a slide block 32 by a pairof guide rails 31 along the X-axis direction arranged on fore and backends of the Y-axis table 5. A screw feed shaft 33 is provided inparallel with the guide rails 31 at the back end of the Y-axis table 5,and rotatably supported by bearings 34. A nut member 35 fixed to theX-axis table 6 is mated with the screw feed shaft 33, which is driven torotate by an X-axis drive motor 36 to cause the X-axis table 6 to movealong the X-axis direction.

The chuck means 7 is mounted approximately in the middle of the X-axistable 6 to pass therethrough to extend downwardly, and comprised of asupport cylinder 27 and a chuck 28 for holding the workpiece 30 coupledto the bottom thereof. The support cylinder 27 extends through anopening 29 formed in the Y-axis table 5 to be elongated in the X-axisdirection to position the bottom surface of the workpiece 30 held by thechuck 28 just above the top surface of the base plate 11. When theY-axis table 5 is brought to the farthest end on the projected part ofthe base plate 11 extending laterally from the main frame 1, the chuck28 comes to position just above the opening 20, through which theworkpiece 30 is fed and taken out.

The workpiece 30 in this embodiment is a scroll vane made of aluminumalloy casting or cast iron for use in a rotary compressor as can be seenfrom FIGS. 7 and 8. The cutting tool 2 a is an end mill for machiningthe vane. The workpiece 30 is held upside down by the chuck 28 and ismachined by the end mill 2 a from below.

Three or more cutting oil nozzles 37 (four nozzles 37 a, 37 b, 37 c, 37d in this embodiment) are disposed at an approximately equal distance inthe vicinity of the opening 19 in the base plate 11 as shown in FIGS. 7and 8, to eject cutting oil to the workpiece 30 being machined by thecutting tool 2 a at the tip of the spindle 2. FIG. 2 shows only one ofthe nozzles in order to simplify the illustration. By providing at leastmore than three cutting oil nozzles 37 around the workpiece 30, itbecomes possible to apply the oil to every part of the workpiece 30.

Each of the four cutting oil nozzles (37 a to 37 d) is connected to anoil pump 45 through four control valves 44 a-44 d, respectively. Thecontrol valves 44 a-44 d are controlled by the numerical control device60 to open and close for supplying oil to the desired one of the cuttingoil nozzles 37 a-37 d depending on where the workpiece 30 being machinedpositions. Since the oil is ejected only from effective nozzles properlyselected, the oil pump 45 of small size can supply a sufficient amountof cutting oil.

Referring again to FIG. 2, a splash guard hood 38 is provided to a skirtof the support cylinder 27 to hang above the top surface of the baseplate 11. Extending downwardly from the opening 19 is an upper cylinder39 of a collecting hopper 40, which is disposed to surround the rotarydriver 3. The collecting hopper 40 is either coupled to or connected bya bellow to the upper cylinder 39 to be movable with respect to eachother, and connected to a collecting duct 41 extending to the outsidefrom a lower part of the body frame 1. The collecting duct 41 is furtherconnected to a vacuum suction means, by which cutting oil and chips aredischarged. The upper cylinder 39 and the collecting hopper 40 may beuniformly constructed, surrounding and allowing the rotary driver 3 tovertically move therein.

The collecting hopper 40 and its upper cylinder 39 are arrangedeccentrically with respect to the rotary driver 3. An air blow means 42for blowing a mixture of cutting oil and chips gathered in thecollecting hopper 40 toward the collecting duct 41 is disposed at a sidewhere a gap made between the periphery of the rotary driver 3 and thesurrounding collecting hopper 40 is narrower, from where the air isejected toward the other side where the gap is wider, so as toeffectively collect and discharge the cutting oil and the chips.

Cutting oil may also be blown out in the above-described way instead ofthe air. The air may be blown into the collecting hopper 40 in atangential direction to create a whirl therein to gather the mixture ofcutting oil and chips. In order to prevent the cutting oil fromsplashing out through a gap at the bottom of the splash guard hood 38, aweir 43 is provided on the base plate 11, which is formed to be a largerectangle so as to avoid interference with the splash guard hood 38 whenthe Y-axis table 5 is moved toward the projected part of the base plate11.

As shown in FIG. 10(a), the corner radius of the cutting tool 2 a ismade equal to a radius R1 of the minimum radius corner 30 a of theworkpiece 30, in order to machine all parts of the workpiece 30including the corners with different radius values with the singlecutting tool 2 a. When machining a corner 30 b with a larger radius R2,the Z-axis drive motor 18 and the Y-axis drive motor 26 or the X-axisdrive motor 36 are controlled by the NC device 60 to cause the cuttingtool 2 a along the radius R2 of the corner 30 b as shown in FIG. 10(b).

The rotary driver 3 comprises a high-speed motor with the spindle 2 asits axis of rotation as shown in FIG. 11. A tool holder 51 supportingthe cutting tool 2 a is fixedly mounted at the top of the spindle 2. Theupper and lower ends of the spindle 2 are supported by magnetic radialbearings 52 and 53. Numerals 52 a and 52 b denote sensors forcontrolling the magnetic radial bearings 52 and 53, respectively. Amotor 54 is comprised of a rotor 55 fixed to the middle part of thespindle and a stator 56. A magnetic thrust bearing 57 is mounted belowthe upper magnetic radial bearing 52, and protective bearings 58 a and58 b are further provided for supporting the spindle 2 when the spindleis at a halt or during its low-speed rotation. Numeral 59 denotes anencoder disposed at the lower end of the spindle 2.

The magnetic radial bearings 52, 53 are constructed with magnetic ringsto have magnetic attraction evenly thereon, so as to support the spindle2 floated in the middle thereof as shown by a solid line in FIG. 12(b).When the spindle 2 is decentered as shown by a phantom line, the amountof displacement from the axial center of the bearings is detected by thesensors 52 a, 53 a, which is converted into signals corresponding toreference signals through a first signal processing means 61. Controlsignals, given by subtracting the converted signals from the referencesignals, are then inputted to a second signal processing means 62, whichconverts the inputted control signals into magnetic attraction controlsignals. The magnetic attraction of the magnetic radial bearings 52, 53are controlled by the magnetic attraction control signals throughamplifiers 63 a, 63 b, to relocate the spindle 2 in the center of thebearings. As can be seen from the arrangement described above, it isalso possible to position the spindle 2 at any given eccentricallocation by varying the reference signals.

Since this embodiment employs the X-axis table 6 and the Y-axis table 5movable along the X- and Y-axes controlled by the numerical controldevice 60 to determine the positions of the workpiece 30 which ismachined by the cutting tool 2 a positioned along the Z-axis direction,an inertial force or adverse effects of a backlash when the X- or Y-axis5, 6 changes the direction sometimes causes an error in machining,creating projections at both ends of the workpiece 30 along the X- andY-axes as shown in FIG. 13. This error is called a “quadrant projection”50, as the projections are usually created at the boundaries of adjacentquadrants in an X-Y coordinate.

To prevent such a quadrant projection 50, the machining operationaccording to this embodiment is carried out in a manner hereinafterdescribed referring to FIG. 14. Firstly, a master work is prepared inadvance at step #1, and the surface contour of the master work ismeasured at step 2. The amount of each quadrant projection 50 is sampledat step 3, from which the amount of correction necessary for positioningthe X-axis table 6 and the Y-axis table 5 for machining is calculated atstep 4. At step 5, the workpiece 30 is machined, and where the quadrantprojection 50 is created, the position of the spindle 2 is adjusted bythe magnetic radial bearings based on the amount of correctioncalculated at step 4. It is thus possible to prevent the quadrantprojections 50 by simply decentering the supporting position of thespindle 2 by the magnetic radial bearings. The operation is therebysimplified as it is no longer necessary to correct the numerical controldata at each point where the X- or Y-axis table changes its direction,yet accomplishing highly precise machining. The method of correctingerrors by adjusting the supporting position of the spindle 2 by themagnetic radial bearings 52, 53 has been described for eliminating thequadrant projections 50 in this embodiment, but this method can also beapplied to correct the errors in surface contour of the workpiece 30caused by lead errors of the screw feed shafts 23, 33 or errors inrectilinear movement of the guide rails 21, 31.

The operation of machining the workpiece 30 will be hereinafterdescribed. Firstly, the Y-axis table 5 is positioned at the projectedpart of the base plate 11 laterally extending from the body frame 1 asshown by a phantom line in FIG. 3 or in FIG. 6. The workpiece 30 is fedto the chuck 28 and received therefrom by a relocating means (not shown)as shown by an arrow. After a workpiece 30 which has been machined isforwarded to a transfer means (not shown) disposed below the projectedpart of the base plate 11, a new workpiece 30 is positioned just underthe opening 20 and transferred to the chuck 28 by the relocating means.

The Y-axis table 5 is then moved to a predetermined position above thebody frame 1, where the Y-axis table 5 and the X-axis table 6 arepositioned so that the machining of the workpiece 30 can be started at aposition just above the axial center of the spindle 2. The spindle 2 isrotated at high speed of 4000 rpm and at the same time lifted upward bythe Z-axis moving means 4 for starting the machining operation of theworkpiece 30 by the cutting tool 2 a at the tip of the spindle 2. Themovements of the Y-axis table 5, the X-axis table 6, and the Z-axismoving means 4 are controlled by the numerical control device 60 toaccurately machine the workpiece 30 in accordance with a predeterminedmachining configuration.

When the machining is finished, the spindle 2 is descended by the Z-axismoving means 4, and the Y-axis table 5 is returned to the projected partof the base plate 11 laterally extending from the body frame 1. Theworkpiece 10 which has been machined is taken out therefrom and a newworkpiece 10 is chucked as described above. The operation of machiningis carried out by repeating these steps.

As set forth above, the machine tool according to the present inventionis constructed with high rigidity in a compact design by disposing ahigh-speed motor as the rotary driver 3 having the built-in spindle 2within the body frame 1 in such a way that the spindle 2 is movablealong the Z-axis direction, thereby realizing high-speed and highlyprecise machining while keeping the entire configuration of the machinetool to be small, contributing to a lower cost and less space forinstallation.

Since the spindle 2 is rotatably supported by non-contact bearingscomprising the magnetic radial bearings 52, 53, a high-speed machiningoperation as fast as 4000 rpm can be carried out. It is thus possible tolessen the rigidity of the body frame, base flame, and each table, sincethe machining force required is reduced as the speed of operationincreases, further contributing to a more compact design manufactured ata lower cost.

The spindle is disposed perpendicular to a horizontal plane andconstructed to be movable only along the Z-axis direction. This enablesthe members such as the splash guard hood 38 or the collecting hopper 40for collecting cutting oil and chips to be vertically disposed. Thesplash guard hood 38 is mounted around the chuck 28, the upper cylinder39 of the collecting hopper 40 extends from the opening 19 of the baseplate 11, and the collecting hopper 40 is disposed to surround thespindle 2 moving along the Z-axis direction. The cutting oil and thechips thus smoothly flow downwardly by gravity into the collectinghopper 40 disposed lowermost and can be effectively collected andprocessed by such a simple configuration.

The method of eliminating the quadrant projections 50 is embodied bydecentering the supporting position of the spindle 2 by the magneticradial bearings 52, 53 in this embodiment, but this method may also bemodified as shown in FIG. 15. As can be seen, the chuck means 7 isprovided with a chuck rotating means 47 to cause the chuck 28 to rotatearound the axial center thereof. The chuck rotating means 47 comprises adrive motor arranged concentrically with the support cylinder 27, havinga rotation axis 48 with the chuck 28 fixed to the bottom end thereof.Numerals 47 a and 47 b denote a rotor and a stator of the drive motor,respectively, and the numeral 49 represents a sensor unit for detectingthe position and speed of rotation.

The above described arrangement enables the workpiece 30 to be machinedby the cutting tool 2 a while rotated around its axial center by thechuck rotating means 47. Any circled parts of the workpiece 30 can bethereby precisely machined without quadrant projections 50.

In the above-described first embodiment, the weir 43 provided on thebase plate 11 to surround the splash guard hood 38 broadly enough not tointerfere therewith has been shown as an example of an arrangement toprevent the cutting oil and the chips from scattering. Since there is agap between the splash guard hood 38 and the upper cylinder 39 of thecollecting hopper 40, sometimes it cannot be fully prevented that thecutting oil and the chips are splashed through the gap over to the baseplate 11. FIG. 16 shows another arrangement for prevention of suchscattering, in which an annular seal plate 64 is provided at the skirtof the splash guard hood 38, and a seal frame 65 is disposed above andalong the circular opening 19 of the base plate 11 which is slidablewith the annular seal plate 64 while keeping the sealing performancetherebetween. The sealing members 64, 65 do not obstruct the movement ofthe chuck means 7 and the splash guard hood 38, yet assuringly seal thegap between the splash guard hood 38 and the upper cylinder 39 of thecollecting hopper 40.

The cutting oil and the chips created during the machining operation canbe thereby prevented from scattering around and be effectivelycollected. Further, such sealing members 64, 65 help prevention ofvacuum leakage when used in combination with the collecting duct 41connected to the vacuum suction means (not shown), and enhances theeffect of vacuum suction for faster and more effective collection of theoil and chips.

It has been basically described that a new workpiece 30 is fed andmachined one after another in the machine tool of the present invention,however, as shown in FIGS. 17(a)-(c), it is also possible to feed aworkpiece 30 having been machined by a different machine tool in aproceeding process shown in FIG. 17(a) to another machine tool asindicated by a center-blanked arrow, which is then held by the chuck 28as shown in FIG. 17(b) and further machined by another type of cuttingtool 2 a. In such a case, there is a disadvantage of inevitable chuckingerrors of approximately 5 μm when the workpiece 30 is held again by thechuck 28, causing greater errors in machining precision. This problem isovercome by a position sensor 66 connected to the NC device 60 shown inFIG. 17(c). After the workpiece 30 already machined by a machine tool ina proceeding process is held by the chuck 28, the chucking position isdetected by the position sensor 66, the result of which is inputted tothe NC device 60. Numerical control data are corrected by the amount ofchucking errors in the NC device 60, according to which the workpiece 30is further machined.

Since the errors caused by chucking operation is eliminated as describedabove, highly accurate machining is possible even when a workpiece 30machined by a different machine tool is fed to another machine tool. Theposition sensor 66 may be provided in plurality so as to detect theposition of the workpiece 30 at several points along the peripherythereof, or may be arranged to be movable around the workpiece 30.Reversely, the workpiece 30 may be arranged to be movable while a singleposition sensor 66 is fixedly mounted. For example, the workpiece 30 maybe held and rotated by the chuck rotating means 47 described withreference to FIG. 15.

FIG. 18 shows another arrangement of a machine tool according to thepresent invention, in which a plurality of chuck means 7 are disposed inthe X-axis table 6 in parallel with each other along the X-axisdirection. A plurality of rotary drivers 3 are supported by the Z-axismoving means 4 disposed in parallel with each other along the X-axisdirection at the same intervals as that of the chuck means 7 in the bodyframe 1. Alternatively, a plurality of chuck means 7 may be provided inthe X-axis table 6 in parallel with each other along the Y-axisdirection, as well as a plurality of rotary drivers 3 may be provided tothe Z-axis moving means 4 disposed in parallel with each other along theY-axis direction at the same intervals as that of the chuck means 7.

A plurality of workpieces 30 can be thereby simultaneously machined,contributing to increase in productivity.

FIG. 19 shows yet another arrangement of the machine tool according tothe present invention, in which a single chuck means 7 is disposed inthe X-axis table 6, while a plurality of rotary drivers 3 are providedto the Z-axis moving means 4 either along the X-axis or the Y-axisdirection. Each rotary driver 3 may be respectively provided with theZ-axis moving means 4, so that each rotary driver 3 can be movedindependent of each other along the Z-axis direction. The positionsensor 66 mentioned above may be provided to the Z-axis moving means 4in place of one of the rotary drivers 3.

By providing several different cutting tools 2 a at the tips of thedifferent spindles 2 in each rotary driver 3, the workpiece 30 needs tobe held by the chuck means 7 only once, and several processes ofmachining can be done to the workpiece 30 in a single machine tool,contributing to increase in productivity.

FIG. 20 shows still further arrangement of the machine tool according tothe present invention, in which the base plate 11 is laterally projectedin the Y-axis direction from both sides of the body frame 1, where theopenings 20 are respectively provided, and a pair of chuck means 7 aredisposed in the X-axis table 6 in parallel with each other along theY-axis direction. The Y-axis table 5 is so constructed that it can betransferred between the farthest ends, where one of the chuck means 7positions above the opening 19 and the other positions above the opening20 in the projected part of the base plate 11.

This arrangement allows for increase in productivity by reduction oftime required for exchanging the workpieces 30, since workpieces 30 canbe fed to and received from the chuck means 7 situated above the opening20 while another workpiece 30 held by another chuck means 7 situatedabove the opening 19 is being machined.

The base plate 11 may not necessarily be projected to one or either sideof the body frame 1 as has been described above, and instead, the bodyframe 1 may be constructed to have the width of the entire base plate11, and provided with the transfer means of the workpiece 30 or therelocating means at one or either side thereof. Also, the spindle 2 maybe designed to be movable along the X-axis direction as well as theZ-axis direction, and the base plate 11 may be provided only with theY-axis table 5 with the chuck 28 for holding the workpiece 30. Further,the magnetic radial bearings 52, 53 may be replaced with any non-contacttype bearings such as air bearings for rotatably supporting the spindle2.

It is to be understood that a machine tool designed to have the spindle2 along a horizontal direction will have the same effects and advantagesas those of the present invention described heretofore, in which thespindle 2 is disposed perpendicular to a horizontal plane.

INDUSTRIAL APPLICABILITY

As set forth above, a machine tool according to the present inventionrealizes highly precise machining yet keeping the entire configurationto be minimized in size, weight, and cost.

Accordingly, the present invention can be advantageously used as amachine tool.

What is claimed:
 1. A machine tool, comprising: a stationary body framehaving an at least partially enclosing structural configuration; aspindle with a central axis and fixedly supported at opposed sideswithin the body frame and located approximately at the center of thebody frame; an X-axis table and a Y-axis table being respectivelymovable in X-axis and Y-axis directions provided on a top face or one offour sides of the body frame and therewith in parallel planes which lieorthogonal to the central axis of the spindle in such a manner as to becumulated on one another; and at least one chuck mounted on an upper oneof the X-axis table and Y-axis table for holding a workpiece, thespindle being adapted for receivably holding a tool at a distal end ofthe spindle for machining the workpiece held with the at least onechuck.
 2. The machine tool according to claim 1, further comprising:guide rails disposed at opposed sides within the body frame; and Z-axismoving means which are slidably supported on the guide rails for movingthe spindle in the Z-axis direction, said spindle being fixed to saidZ-axis moving means.
 3. The machine tool according to claim 2, whereinthe body frame is constructed to have an approximately U-shaped crosssection and the guide rails are disposed in the body frame in such amanner that the entire construction of the machine tool appearsapproximately symmetrical in a cross section around an axis of symmetrybetween the guide rails.
 4. A machine tool according to any of claims 1to 3, further comprising a base plate provided on the top face or one offour sides of the body frame, the base plate having an opening thereinopposite to the spindle through which operation is carried out, andsupporting at least one of the X-axis and Y-axis tables disposedthereon.
 5. A machine tool according to claim 4, wherein: the base plateincludes another opening; the X-axis table with said at least one chuckmounted thereto is carried on the Y-axis table; and the Y-axis table ismovable between a position immediately above the opening in the baseplate and a position laterally away therefrom where said another openingis provided through which a workpiece is removed from and fed to the atleast one chuck of the Y-axis table.
 6. A machine tool according toclaim 5, wherein the Y-axis table is retractable to a farthest end ofthe base plate laterally extending from one side of the body frame asufficient distance to provide a clear space above the opening in thebase plate for operation.
 7. A machine tool according to claim 5,wherein the base plate is extended toward at least one of two sides ofthe body frame, where said another opening is formed for feeding aworkpiece to the at least one chuck of the Y-axis table and receivingthe same therefrom.
 8. A machine tool according to any of claims 1 to 3,further comprising a base plate provided on the top face or one of foursides of the body frame, the base plate having an opening thereinopposite to the spindle through which operation is carried out, and atleast one of said X-axis and Y-axis tables disposed above the bodyframe, wherein the spindle is arranged to have the axis thereof along avertical direction and mounted with a cutting tool at a tip thereof, andthe at least one chuck is designed to hold a workpiece downwardly.
 9. Amachine tool according to any of claims 1 to 3, wherein the spindle isbuilt in a high-speed motor as a rotary driver thereof and rotatablysupported by non-contact type bearings.
 10. A machine tool according toclaim 9, wherein the non-contact type bearings are magnetic radialbearings.
 11. A machine tool according to claim 9, further comprisingmeans for correcting errors in machining the workpiece by adjusting asupporting position of the spindle supported by the non-contact typebearings.
 12. A machine tool according to claim 1 or 2, furthercomprising a chuck rotating means for causing the at least one chuck torotate around the axis thereof.
 13. A machine tool according to claim 1or 2, wherein the body frame is constructed to have an approximatelyU-shaped cross-section.
 14. A machine tool according to claim 1 or 2,further comprising a position sensor for detecting position of theworkpiece held by the at least one chuck.
 15. A machine tool accordingto claim 8, further comprising: a cutting oil applying means forejecting cutting oil from one side of the opening toward the workpiecebeing machined; and a collecting hopper for gathering the cutting oiland chips flowing down thereto.
 16. A machine tool according to claim15, further comprising a splash guard hood provided around the chuckmeans for causing the cutting oil splashing around the workpiece beingmachined to flow down into the collecting hopper.
 17. A machine toolaccording to claim 16, further comprising sealing means to seal a gapbetween the splash guard hood and the collecting hopper while allowing arespective movement with each other therebetween.
 18. A machine toolaccording to claim 15, further comprising: a collecting duct; and acollecting fluid applying means for ejecting a collecting fluid towardinto the collecting hopper, which is connected to the collecting duct.19. A machine tool, comprising: a stationary body frame having an atleast partially enclosing structural configuration; a spindle with acentral axis and fixedly supported at opposed sides within the bodyframe and located approximately at the center of the body frame; anX-axis table and a Y-axis table being respectively movable in X-axis andY-axis directions provided on a top face or one of four sides of thebody frame and therewith in parallel planes which lie orthogonal to thecentral axis of the spindle in such a manner as to be cumulated on oneanother; at least one chuck mounted on an upper one of the X-axis tableand Y-axis table for holding a workpiece, the spindle being adapted forreceivably holding a tool at a distal end of the spindle for machiningthe workpiece held with the at least one chuck; a base plate provided onthe top face or one of four sides of the body frame, the base platehaving an opening therein opposite to the spindle through whichoperation is carried out, and at least one of said X-axis and Y-axistables disposed above the body frame, wherein the spindle is arranged tohave the axis thereof along a vertical direction and mounted with acutting tool at a tip thereof, and the at least one chuck is designed tohold a workpiece downwardly; cutting oil applying means for ejectingcutting oil from one side of the opening toward the workpiece beingmachined; a collecting hopper for gathering the cutting oil and chipsflowing down thereto; collecting fluid applying means for ejecting acollecting fluid toward into the collecting hopper, which is connectedto a collecting duct; and the collecting hopper being arrangedeccentrical with respect to the opening in the base plate, and thecollecting fluid applying means being disposed in such a way that thecollecting fluid is blown from one side where a gap between theperiphery of a rotary driver for rotating the spindle and the collectinghopper is narrow toward another side wide is more widely gapped, wherethe collecting duct is connected to the collecting hopper.
 20. A machinetool according to claim 19, further comprising vacuum sucking means, thecollecting duct connected to the collecting hopper being furtherconnected to the vacuum sucking means.
 21. A machine tool according toclaim 15, wherein the cutting oil applying means comprises at leastthree cutting oil ejecting nozzles disposed to surround the workpiecebeing machined.
 22. A machine tool according to claim 21, furthercomprising an on-off controller for controlling ejection of the cuttingoil from each cutting oil ejecting nozzle in accordance with a positionof the workpiece.
 23. A machine tool according to claim 1 or 2, whereina corner of a workpiece having a given radius is machined by numericalcontrol using a cutting tool designed to machine another corner of theworkpiece having a minimum radius.
 24. A machine tool according to claim1 or 2, wherein a plurality of spindles are arranged in the body frame,and a plurality of chucks are disposed on at least one of the X-axis andY-axis tables.
 25. A machine tool according to claim 1 or 2, wherein thespindle is provided in the body frame in singularity while a pluralityof chucks are disposed on at least one of the X-axis and Y-axis tables.26. A machine tool according to claim 1 or 2, wherein a plurality ofspindles are arranged in the body frame while the at least one chuck isdisposed on one of the X-axis and Y-axis tables in singularity.
 27. Amachine tool, comprising: a stationary body frame having an at leastpartially enclosing structural configuration; a spindle with a centralaxis and fixedly supported at opposed sides within the body frame andlocated approximately at the center of the body frame; an X-axis tableand a Y-axis table being respectively movable in X-axis and Y-axisdirections provided on a top face or one of four sides of the body frameand therewith in parallel planes which lie orthogonal to the centralaxis of the spindle in such a manner as to be cumulated on one another;and at least one chuck mounted on an upper one of the X-axis table andY-axis table for holding a workpiece, the spindle being adapted forreceivable holding a tool at a distal end of the spindle for machiningthe workpiece held with the at least one chuck; a base plate provided onthe top face or one of four sides of the body frame, the base platehaving an opening therein opposite to the spindle through whichoperation is carried out, and supporting at least one of the X-axis andY-axis tables disposed thereon, the base plate including at leastanother opening, the X-axis table with said at least one chuck mountedthereto being carried on the Y-axis table, the Y-axis table beingmovable between a position immediately above the opening in the baseplate and a position laterally away therefrom where said another openingis provided through which the workpiece is removed from and fed to theat least one chuck of the Y-axis table; and said at least one chuckincludes a pair of chucks disposed in the X-axis table in parallel witheach other along the Y-axis direction, and the Y-axis table is arrangedto be movable between farthest ends where one of the pair of chuckspositions just above the opening in the base plate, said at leastanother opening in the base plate including a pair of another openingsthrough which the workpiece is removed from and fed to another of thepair of chucks when the Y-axis table is located at a given one of saidfarthest ends.